1. Field of the Invention
The present invention relates to an image display apparatus and a drive method to operate the display apparatus. The display apparatus comprises a light source and a light modulator that modulates the light from the light source to produce images. The display apparatus further comprises a control means for operating the light source and the light modulator. The control means operates the light source and the light modulator in coordination, and in such a manner that enhances the response time of the light modulator. Furthermore, the light source comprises light emitting elements with response time substantially faster than the relaxation time of the light modulator, and is operated in such a manner that eliminates the adverse effects from switching the light modulator.
2. Description of the Prior Art
A liquid crystal (LC) cell is a light valve that modulates light directed thereto. A liquid crystal display (LCD) produces images by modulating light with a plurality of spatially distributed LC cells. The LC cells in a display are set to various states according to the spatially distributed color and brightness of the image, and varying in time in motion pictures. The capability of showing motion pictures of such display device is influenced by the speed of the LC cell responding to the change of setting of state when the image changes. Accordingly, the response time, which characterizes the speed of an LC cell responding to a change of setting, is a speed limitation of the LC cells in displaying dynamic images.
In displaying motion pictures, the cell setting is updated at a rate at least the refreshing rate of the picture images. In addition, in different applications such as color sequential drive scheme, an LC response time much higher than the image refreshing rate is needed. Accordingly, a response of the LC cell slower than the rate of the changing images results in various types of distortion and artifacts in images, such as color breakup, trailing of a moving object, flicker and etc.
Furthermore, the current LC display relies on the color filters to produce color images. Each color filter inhibits the transmission of the other colors. Consequently, in a color display where display cells are structured with three primary colors, the efficiency of light utilization due to the color filter alone drops to below 30%. An alternative is to structure the display without color filters and operate the display by sequentially displaying the color image components corresponding to different colors in time, thereby producing a time-integrated replication of the input color images. In the conventional practice of such color-sequential drive scheme, the LC cells are operated at a speed three times faster than that of LC cells operated with three color filters are used. Typical liquid crystal cell structures used in consumer direct-view displays have a cell gap near 5 micrometers and an intrinsic response time above 8 milliseconds; the response time is much longer when the action is directed toward a relaxation. Such response time is not sufficient for operating an acceptable time-integration of color sequenced images which requires a response time on the order of 1 ms or faster. Consequently, sequencing three colors in time is not yet a viable solution to improve the light and power efficiency in such applications. Other proposed schemes such as using two-color sequence also result in images compromising in quality or suffering inherent color deficiency at various situations and picture types.
The present invention provides an apparatus and method to improve or eliminate the aforementioned artifacts and distortion, and to provide a method to operate the LC cells at a faster intrinsic response time. Accordingly, direct viewing LC display may be constructed and operated without color filter, and at an improved efficiency.
As the response is generally slower from a charged state to a relaxed state than in the opposite direction in many light valves, such as LC cells and MEMS, the present invention is directed to the application to the light valves in general, with LC cell as a preferred embodiment for the purpose of illustration in this specification.